Answers to moral questions, it seems, depend on how much serotonin there is flowing through your brain. In the future might we be able to alter people's moral behaviour with concoctions of chemicals? A train is hurtling towards five people; it's out of control. You are standing on a footbridge, standing next to a very obese man. The only way to save the five is to push the man over the footbridge to his certain death: his bulk would stop the train and save five lives. Should you do it? Should you give him a shove? Most people would say no. Utilitarians say yes, you should take one life to save five. Now it turns out that the answer you give will depend on how much serotonin there is flowing through your brain. This raises an intriguing possibility: in the future might we be able to alter people's moral behaviour with concoctions of chemicals? That's been the research focus of Molly Crockett, now based in Zurich, but formerly of Cambridge University